It is standard to roll steel profiles--I-beams, H-beams, and the like--in a rolling string comprised of a succession of universal roll stands each having a pair of horizontal working rolls that engage the top and bottom surfaces of th profile and a pair of vertical working rolls that engage its sides. Each time the workpiece passes through such a universal stand at least one of its vertical or horizontal dimensions is reduced and the workpiece mass distribution is changed, typically its length is augmented.
In fact as the rolling operation progresses the relative amounts of vertical and horizontal compression and, hence, of elongation change, thereby also changing the ratio between the peripheral speeds of the vertical and horizontal rolls. As a result in the same universal roll stand the workpiece can be subjected to uncontrollable changes in cross section resulting in substantial internal stresses caused by lateral shifts of material as the workpiece is being rolled. Such lateral material flow is not desired; instead the flow is supposed to be longitudinal for the desired longitudinal grain orientation that imparts the desired strength to the workpiece.
As a rule the horizontal rolls are positively driven, but the vertical rolls have no drives and in fact ar rotated by engagement with the workpiece so that in effect they idle. It is normally considered impossible to provide drives for the vertical rolls due to space limitations. Even when the peripheral speeds of the vertical rolls are generally stable at a predetermined level relative to the peripheral speeds of the horizontal rolls of the same stand, substantial problems in the overall movement of the workpiece through the succession of roll stands result in a changing peripheral-speed ratio as rolling progresses. Even changes in the tension exerted in the strand from one roll stand to the next are reflected in the peripheral speeds and also in the material flow. Also such peripheral-speed ratio changes result in accelerations of the horizontal rolls and the material of the workpiece can affect the ratio of the peripheral speeds of the horizontal and vertical rolls.
Such material-flow changes caused by the change in the speed ratios are not wanted. Since the workpiece volume does not change it is necessary for the material to flow transversely when it cannot elongate. The result can therefore be a workpiece that varies in cross-sectional measurements, a clearly unacceptable product as it is impossible to control whether this transverse material flow is taking place in the desired locations or not. In addition the prior-art systems can lead to the production, from blanks of the same volume, of workpieces of different lengths and workpieces having, for instance, one flange that is wider than the other when the workpiece is supposed to be symmetrical.